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排序方式: 共有428条查询结果,搜索用时 31 毫秒
91.
Gunnar Brinkmalm Erik Portelius Annika Öhrfelt Niklas Mattsson Rita Persson Mikael K. Gustavsson Charles H. Vite Johan Gobom Jan‐Eric Månsson Jonas Nilsson Adnan Halim Göran Larson Ulla Rüetschi Henrik Zetterberg Kaj Blennow Ann Brinkmalm 《Journal of mass spectrometry : JMS》2012,47(5):591-603
Amyloid precursor protein (APP) is the precursor protein to amyloid β (Aβ), the main constituent of senile plaques in Alzheimer's disease (AD). Endogenous Aβ peptides reflect the APP processing, and greater knowledge of different APP degradation pathways is important to understand the mechanism underlying AD pathology. When one analyzes longer Aβ peptides by low‐energy collision‐induced dissociation tandem mass spectrometry (MS/MS), mainly long b‐fragments are observed, limiting the possibility to determine variations such as amino acid variants or post‐translational modifications (PTMs) within the N‐terminal half of the peptide. However, by using electron capture dissociation (ECD), we obtained a more comprehensive sequence coverage for several APP/Aβ peptide species, thus enabling a deeper characterization of possible variants and PTMs. Abnormal APP/Aβ processing has also been described in the lysosomal storage disease Niemann–Pick type C and the major large animal used for studying this disease is cat. By ECD MS/MS, a substitution of Asp7 → Glu in cat Aβ was identified. Further, sialylated core 1 like O‐glycans at Tyr10, recently discovered in human Aβ (a previously unknown glycosylation type), were identified also in cat cerebrospinal fluid (CSF). It is therefore likely that this unusual type of glycosylation is common for (at least) species belonging to the magnorder Boreoeutheria. We here describe a detailed characterization of endogenous APP/Aβ peptide species in CSF by using an online top‐down MS‐based method. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
92.
Lucas Wickemeyer Niklas Aders Andreas Mix Beate Neumann Hans-Georg Stammler Jorge J. Cabrera-Trujillo Israel Fernndez Norbert W. Mitzel 《Chemical science》2022,13(27):8088
The reaction of tBu2P(O)H with Bis2AlH (Bis = CH(SiMe3)2) afforded the adduct tBu2P(H)–O–Al(H)Bis2 (3). It slowly releases H2 to form the first oxygen-bridged geminal Al/P frustrated Lewis pair tBu2P–O–AlBis2. It is capable of reversibly binding molecular hydrogen to afford 3, shown by NMR and H/D scrambling experiments, and forms a 1,2-adduct with CO2. Importantly, the H2 adduct 3 reduces CO2 in a stoichiometric reaction leading to the formic acid adduct tBu2P(H)–O–Al(CO2H)Bis2. The formation of the different species was explored by density functional theory calculations which provide support for the experimental results. All products were characterized by NMR spectroscopy as well as X-ray diffraction experiments and elemental analyses.Addition vs. reduction: the geminal FLP Bis2Al–O–PtBu2 can reversibly bind molecular hydrogen, it reacts with CO2 to give an adduct, and its hydrogen adduct reduces CO2 to an adduct of formic acid. 相似文献
93.
Dr. You-Quan Zou Dr. Niklas von Wolff Dr. Michael Rauch Dr. Moran Feller Dr. Quan-Quan Zhou Dr. Aviel Anaby Dr. Yael Diskin-Posner Dr. Linda J. W. Shimon Dr. Liat Avram Yehoshoa Ben-David Prof. Dr. David Milstein 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(14):4715-4722
Glycolic acid is a useful and important α-hydroxy acid that has broad applications. Herein, the homogeneous ruthenium catalyzed reforming of aqueous ethylene glycol to generate glycolic acid as well as pure hydrogen gas, without concomitant CO2 emission, is reported. This approach provides a clean and sustainable direction to glycolic acid and hydrogen, based on inexpensive, readily available, and renewable ethylene glycol using 0.5 mol % of catalyst. In-depth mechanistic experimental and computational studies highlight key aspects of the PNNH-ligand framework involved in this transformation. 相似文献
94.
Niklas O. Thiel Benyapa Kaewmee Trung Tran Ngoc Prof. Dr. Johannes F. Teichert 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(7):1597-1603
Stereoselective alkyne semihydrogenations are attractive approaches to alkenes, which are key building blocks for synthesis. With regards to the most atom-economic reducing agent dihydrogen (H2), only few catalysts for the challenging E-selective alkyne semihydrogenation have been disclosed, each with a unique substrate scope profile. Here, we show that a commercially available nickel catalyst facilitates the E-selective alkyne semihydrogenation of a wide variety of substituted internal alkynes. This results in a simple and broadly applicable overall protocol to stereoselectively access E-alkenes employing H2, which could serve as a general method for synthesis. 相似文献
95.
G. White J. Rikovska N. J. Stone J. Copnell I. S. Towner A. M. Oros K. Heyde B. Fogelberg L. Jacobsson F. Gustavsson 《Nuclear Physics A》1998,640(3-4):322-336
On-line low temperature nuclear orientation (OLNO) experiments have been performed on the odd-A Te isotopes 131Te and 133Te using the technique of nuclear magnetic resonance on oriented nuclei (NMR/ON). The magnetic moments of the isomeric 11/2− states have been measured extending the known data on these states in the Te isotopes up to the neutron shell closure at N = 82. The contribution to the 11/2− magnetic moment in 133Te due to core polarisation is calculated using an RPA shell model as well as corrections to the magnetic dipole operator caused by mesonic exchange currents. The neutron number dependence of the magnetic moments of the 11/2− isomers in heavy Te isotopes is discussed in terms of particle-core coupling model (PCM) calculations. 相似文献
96.
97.
Densitometric quantification of individual phospholipids. Improvement and evaluation of a method using molybdenum blue reagent for detection 总被引:1,自引:0,他引:1
L Gustavsson 《Journal of chromatography. A》1986,375(2):255-266
A densitometric method for simultaneous quantification of individual phospholipids based on visualization with molybdenum blue reagent is presented. Previously reported problems concerning colour instability have been solved. The method is specific for phosphorus-containing compounds and independent of the degree of fatty acid unsaturation. The molar absorptivities of most analysed phospholipids do not differ more than 10% from that for phosphatidylcholine from egg yolk. For cases of greater deviation (sphingomyelin, lysophosphatidylcholine and phosphatidylserine), analysis is accomplished by use of appropriate standard mixtures. The between-series coefficient of variation is ca. 9%. The method is compared to a preparative thin-layer chromatographic assay and another commonly used densitometric method. 相似文献
98.
Anders Holmbom Jeanette Silfver Nils Svanstedt Niklas Wellander 《Applications of Mathematics》2006,51(3):247-262
A general concept of two-scale convergence is introduced and two-scale compactness theorems are stated and proved for some
classes of sequences of bounded functions in L
2(Ω) involving no periodicity assumptions. Further, the relation to the classical notion of compensated compactness and the
recent concepts of two-scale compensated compactness and unfolding is discussed and a defect measure for two-scale convergence
is introduced. 相似文献
99.
A. Niklas 《Applied physics. B, Lasers and optics》1984,34(2):87-92
The spectral distribution of the thermoluminescence (TL) of YAG:Nd crystals coloured by x-ray irradiation at room temperature (RT) and at 80 K has been investigated. The spectral distribution of TL in the uv-, visible and near ir ranges shows that the energy transfer by bound exciton states (BES) to the RE3+ ions (Nd3+ and Tb3+) decreases with increasing temperature. The TL spectrum in the uv range is ascribed to the hole defect centers. Diminution of the energy transferred by the BES to the Nd3+ and Tb3+ ions is the direct cause for the occurrence of the group of lines ascribed to the Nd3+ ions in TL observed at LT, whereas at RT and higher only the groups of Tb lines are observed. 相似文献
100.
J. Persson U. Berzinsh T. Nilsson M. Gustavsson 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1992,23(1):67-70
The hyperfine structure of the metastable atomic states 5d 36s 2 4 P 3/2 and4 P 5/2 in181Ta has been studied using high resolution laser spectroscopy and laser radio-frequency double-resonance methods. 相似文献